The present invention relates to a mesh screen of polyester filaments for screen printing or, more particularly, to a mesh screen of polyester filaments for screen printing imparted with greatly improved adhesion with the layer of a photosensitive resin for patterning without decrease in the mechanical strength of the mesh screen.
Screen printing is a type of stencil printing using a patterned mesh screen as the printing screen. Thus, a mesh screen of fine filaments spread over a frame is coated with a photosensitive resinous composition to fill the meshes and the coating layer is exposed pattern-wise to light to cure the resin in the exposed areas followed by removing the resin composition from the unexposed areas to give a patterned printing screen composed of the areas of open meshes and areas of filled meshes. A printing ink is forced through the open meshes by means of a rubber roller and the like and transferred on to a material to be printed, e.g., paper, to complete the desired printing.
The filaments forming the mesh screen can be made of a variety of materials including silk, nylon, polyester, stainless steel and the like, of which polyester filaments are more and more preferred in recent years by virtue of the inexpensiveness and good recovery of elastic resilience.
Mesh screens made of polyester filaments are, however, not free from several problems. For example, the surface of a polyester filament is relatively smooth and has low affinity with water as compared to other materials above mentioned so that the adhesion of the photosensitive resin composition to the mesh screen is not always quite strong. This means that the photocured resinous coating layer may sometimes fall off the screen in the course of screen preparation and during use of the patterned mesh screen as a printing screen. This problem is particularly serious when the pattern formed on the screen is fine. Such a problem of falling of the resinous coating layer can occur in the development treatment after pattern-wise exposure of the coating layer to light or in the course of the printing works using the patterned screen in which the screen is cleaned by using an organic solvent or the screen is repeatedly subjected to a considerably large pressing action by a rubber-made squeezer which forces the printing ink through the open meshes of the patterned screen on to paper and the like.
Various attempts and proposals have been made hitherto to solve the above mentioned problem by the falling of the resinous layer including chemical treatments using various kinds of chemicals, flame treatment and so on. These prior art methods are not quite satisfactory in respect of the improvement thereby in the adhesion between the resinous coating layer and the polyester mesh filaments. Even worse, these prior art methods may sometimes cause an undue decrease in the mechanical strength of the filaments so that the mesh screen is subject to a danger of breaking in the spreading over a frame or during the printing works. For example, the mesh screen may be readily broken when it is contacted with a cornered body.